This invention relates to an exhaust gas for cleaning by repeated reactions of the exhaust gases from an internal combustion engine, and more specifically, to one for cleaning the exhaust gas by passing the same through a catalyst and thereby effecting re-reaction in the catalyst bed with the heaat retained by the exhaust itself.
Many diversified researches have been done in the technical field of exhaust gases purifying. To effectively operate the exhaust gas cleaning device using the catalyst under varying operative condition, it is necessary to keep the catalyst at a very high temperature so that full catalytic action can be sufficiently attained. This is of particular importance in the cold start of the engine. Even after the warmup, the temperature of the exhaust gas leaving the engine drops so rapidly that a catalyst converter if installed downstream the exhaust line would fail to function satisfactorily because of the lowered exhaust temperature. If the quantity of the catalyst is increased to make up for the loss of its activity, the temperature rise of the catalyst as a whole will be delayed. Thus, in either case, it is often difficult to attain the end with the known devices. Various attempts have been made to overcome these difficulties, but none has proved quite successful.
Moreover, the life of the catalyst is not indefinite. To ensure positive purifying of the exhaust gases, the catalyst must be replaced from time to time. Consideration should, therefore, be given to improvements in the replaceability of the catalyst and in the serviceability of the device. According to the prior art in order to improve the replaceability and serviceability, a catalyst-containing package is disposed between the exhaust manifold and the exhaust pipe. Another attempt was to install such a package on the exhaust manifold. However, the engine room of a vehicle carrying an internal combustion engine therein also accommodates safety and other auxiliary devices, so that the engine room has very little space for location of the catalyst-containing package. For this reason, installation of a catalyst-containing package unit in the engine compartment must be avoided wherever possible.